The traditional implantable cardiac pacemaker includes a pulse generator device to which one or more flexible elongate lead wires are coupled. The device is typically implanted in a subcutaneous pocket, remote from the heart, and each of the one or more lead wires extends therefrom to a corresponding electrode, coupled thereto and positioned at a pacing site, either endocardial or epicardial. Mechanical and/or MRI compatibility issues, which are sometimes associated with elongate lead wires and well known to those skilled in the art, have motivated the development of implantable cardiac pacing devices that are wholly contained within a relatively compact package, the entirety of which is configured for implant in close proximity to the pacing site. FIG. 1 is a schematic diagram that shows potential cardiac implant sites for such a device, for example, within an appendage 102 of a right atrium RA, within a coronary vein CV (via a coronary sinus ostium CSOS), or in proximity to an apex 103 of a right ventricle RV, for example, as shown in FIG. 2.
FIG. 2 illustrates an exemplary relatively compact implantable medical device 100 having been delivered through a catheter 200, which an operator has maneuvered up through the inferior vena cava IVC and the right atrium RA into the right ventricle RV. Device 100 and catheter 200 may be similar to the device and tool, respectively, described in the commonly assigned United States Patent Application US 2015/0094668. Device 100 is shown fixed at an implant site by a fixation member 115 thereof, but still secured to catheter 200 by a flexible tether 280 that extends out from distal opening 203 of catheter 200, being joined to a holding member 121 of device 100. Thus, the operator, via tether 280, is able to test the fixation of device 100 at the implant site, and/or remove device 100 from the implant site for repositioning at a more suitable site, if necessary. Once satisfied with the implant of device 100, the operator can separate tether 280 from device 100, for example, by releasing an end of one length 281 of tether 280, and then pulling on an end of another length 282 of tether 280 to withdraw an entirety of length 282 proximally through delivery catheter 200 so that tether length 281 is pulled distally and through device holding member 121.
Securing device 100 to catheter 200 with tether 280 is typically accomplished by a process in which tether 280 is looped through device holding member 121, after which first and second lengths 281, 282 of tether 280 are threaded through one or more lumens of catheter 200 such that opposing ends thereof protrude out from a proximal opening 201 of catheter 200. Because this process may be somewhat tedious a manufacturer of device 100 and catheter 200 may secure the two together as a system, and provide the system to the operator in a single sterile package. However, due to shelf life considerations, the packaging of such a device separately from the associated catheter may be preferred, so that alternative means for securing the device to the catheter may be necessary to increase the ease by which an operator may load the device into the catheter at the time of an implant procedure.